Prepare Alvar for MultiToe's Brew.
ATTENTION: This will propably not build on MS Windows anymore.

	* Removed build folder (including find modules)
	* Made welcome message optional
	* Fixed several warnings
	* Added untested replacement for CLOCK_MONOTONIC on OS X
	* Stripped CMakeList of samples, osg and tests
	* Let libraries install in folder <prefix>/lib
	* Let headers install in <prefix>/include/alvar